There has conventionally been a refrigeration apparatus constituted by a refrigerant circuit in which a compressor, a condenser, a liquid receiver, an expansion valve, and an evaporator are connected in order by pipes (see, for example, Patent Literature 1).
In some refrigeration apparatuses of this type, a solenoid valve is provided between the liquid receiver and the expansion valve, a pressure sensor is provided on a suction side of the compressor, and a temperature sensor is provided in a cooling target space near the evaporator. When the temperature in the cooling target space detected by the temperature sensor becomes lower than a predetermined value, the solenoid valve closes and refrigerant is collected in the liquid receiver (pump-down). When the pressure detected by the pressure sensor becomes lower than a predetermined value, the compressor stops. When the temperature in the cooling target space detected by the temperature sensor and the pressure detected by the pressure sensor become higher than the predetermined values, the solenoid valve opens and the compressor is operated.
As refrigerant for circulating through the refrigerant circuit of the refrigeration apparatus of this type, a low-GWP (global warming potential) refrigerant has recently been developed to suppress the influence on global warming. Although an HFC (hydrofluorocarbon)-based refrigerant (for example, R410A, R404A, R407C, R134a) used conventionally has high performance, the GWP thereof is high (for example, the GWP of A410A is about 2000). Accordingly, a fluoropropene-based (HFO-based) refrigerant, such as R1234yf, has been developed to further lower the GWP. However, since this refrigerant has a high boiling point and low performance, there are many technical problems in efforts to maintain performance equal to that of the conventional refrigerant, leading to an increased cost.
A refrigerant having a low GWP and a low boiling point (for example, HFO1123) has thus been proposed (see, for example, Patent Literature 2).
It is known that HFO1123 has little influence on the ozone layer because its composition does not contain a chlorine atom, has little influence on global warming because it has a double bond and has a short atmospheric lifetime, and is excellent in performance (capacity) (low-boiling refrigerant). Further, HFO1123 belongs to a flammability classification corresponding to Rank 2L (mildly flammable) according to ASHRAE, and this provides safety.
As described above, HFO1123 (CF2=CHF) is a high-performance refrigerant. On the other hand, it is known that a disproportional reaction (self-decomposition reaction) occurs therein under a specific condition. A disproportional reaction refers to a chemical reaction in which two or more molecules of the same kind react to each other to generate products of two or more different kinds.
The disproportional reaction of HFO1123 is the following chemical reaction:CF2=CHF→(½)CF4+(3/2)C+HF+(reaction heat).
This disproportional reaction is caused by the application of not less than a predetermined amount of energy to the refrigerant, and occurs in chains in a high-pressure environment.